Building a DIY LED from SiC

Wohoo, that are many abbreviations in the title. What this article is about is making a light emitting diode (LED) from a pin and the mineral Moissanite. Moissanite is Silicon Carbide or Carborundum (compound of Silicon and Carbon- SiC) and since it is such a rare substance I used a synthetic form of it. Most of you will know this substance as the black “sand” splinters on sand paper. Due to its extreme hardness it is most often used in abrasive substances and tools. You could easily cut glass with it. I picked up four boxes with 1 cm big crystals for one Euro total on Ebay.

Box of silicon carbide crystals.
Single crystals and pliers as size comparison.

That this material- besides its strength- has another impressive property was discovered by H.J. Round, an american radio engineer in 1907. While experimenting with it as a diode substance in a radio transmitter, he noticed a glow at the contact point of a wire and the silicon carbid. This was the first “LED” known to man. While Round only published a short note on it, a russian physicist named Oleg Losev properly described the properties of this phenomenon and is credited as the inventor of the LED. ¬†While reading his biography I stumbled ¬†upon an article in Nature:Photonics, where the history of the LED is “illuminated”. This got me to try to build an LED myself.

The setup is very simple. I took a crystal of SiC and attached a clamp to it to supply it with about 20 Volts. It is important that the plus clamp is used. It is further advisable to limit the current to something around 30 mA. This will prevent the crystal from heating up too much, as the diode forward voltage will be only on the order of 9 Volts @ 30 mA. If you have no current limiter on your power supply or want to use a battery, use 12 Volts as fixed voltage and be careful not to overheat your setup. The negative lead is attached to a wire which holds a regular pin from your sowing supplies. After applying the voltage the pin should be moved across the surface forming a cat’s whisker detector. Every now and then a tiny light appears at the contact point. This is the LED! Depending on the site and the current flowing it can be orange, yellow or green and can potentially be relatively bright. To find a perfect spot is however difficult. If you want to replicate the experiment and don’t see a thing, check whether the room is dark enough, the polarity of the leads, the voltage and- if nothing helps- use the side of the needle and trace the edge of the crystal. The current will be higher and so will be the chance of finding a good spot. I also found cracks in larger crystal surfaces to be rewarding. Here are two pictures of the whole thing:

Setup of a home made cat’s whisker detector from SiC and a pin.
The green glow of the DIY LED! At the contact point of pin and crystal greenish light is emitted.

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Thursday, May 7th, 2009 Electronics, Science 5 Comments